获取页面高度
function getPageHeight(){
    var g = document, a = g.body, f = g.documentElement, d = g.compatMode == "BackCompat"
                    ? a
                    : g.documentElement;
    return Math.max(f.scrollHeight, a.scrollHeight, d.clientHeight);
}
获取页面可视宽度
function getPageViewWidth(){
    var d = document, a = d.compatMode == "BackCompat" ? 
                       d.body: d.documentElement;
    return a.clientWidth;
}
获取页面宽度
function getPageWidth(){
    var g = document, a = g.body, f = g.documentElement, d = g.compatMode == "BackCompat"?
                          a: g.documentElement;
    return Math.max(f.scrollWidth, a.scrollWidth, d.clientWidth);
}